An automobile engine anti-freeze coolant, also called antifreeze for short, is mainly composed of an antifreeze agent, an inhibitor, a buffer, a colorant, a defoamer, water and the like, is liquid that has cooling, anti-corrosion, anti-cavitation, anti-scaling, anti-boil and anti-freeze functions and the like and meets the working requirements of liquid-cooled engines at low temperatures, and is an indispensable heat dissipation medium for normal operation of automobile engines.
The antifreeze agent, as a main component, accounts for 92-98% of the antifreeze. Nearly all countries have adopted ethylene glycol as the antifreeze agent since 1950s; the freezing point is influenced by the concentration of the ethylene glycol, and is controlled within an appropriate range by mixing the ethylene glycol with water in a ratio based on local temperature: 40% ethylene glycol by mass is generally adopted in the south of China, while about 50% ethylene glycol by mass is relatively appropriate in the cold north.
The inhibitor is mainly used for preventing the ethylene glycol antifreeze from corroding cooling system materials (composed of copper, aluminum, cast iron, steel, solder, etc.) under high-temperature conditions, thus leading to decline of thermal conductivity of engines, blockage of cooler tubes and overheating of the engines. Inhibitors are divided into two classes: one is inorganic inhibitors, e.g., metasilicate, phosphate, borate, nitrite, molybdate, benzoate, etc.; and the other is organic inhibitors, e.g., common triethanolamine, benzotriazole, organic phosphate, etc. Multiple inhibitors need to be compounded to thoroughly prevent rust in the presence of multiple metals. The antifreeze available in the market and used in foreign patents all adopts a compound of multiple corrosion inhibiting matters, so the corrosion inhibiting rate is high; and the inhibitor accounts for 0.5-5% of the antifreeze by mass.
The buffer is used for stabilizing the pH value of the antifreeze to be 7.5-10, thereby avoiding decline of the pH value and the corrosion inhibiting effect caused by medium acidification; and the common buffer is borate and phosphate. The common defoamer is silicone, alcohols and glycidyl ether, and is 0.001-0.1% by mass. The colorant differs from common cooling water, facilitates observation of leakage of the antifreeze in an engine cooling system, also serves as an acid-base indicator, often adopts bromine methyl blue, phenol red, methyl red, etc., and is generally 0.01-0.05% by mass.
More than 90% of commercial automobile antifreeze adopts ethylene glycol as a main antifreeze agent at present. The ethylene glycol is colorless, odorless and slightly sweet liquid, and is an important basic chemical raw material. The oral lethal dose of the ethylene glycol is 80-100ml, the ethylene glycol may damage the central nervous system, gastrointestinal tract and renal functions, and the toxic symptoms are mainly caused by ethylene glycol metabolites. The general replacement cycle of the automobile antifreeze is 2 years or 60,000 kilometers, the annually replaced waste antifreeze is 450,000-600,000 tons based on 150 million automobile population in China at the end of 2014 (the consumption of antifreeze is 6-8 Kg per vehicle, and the replacement cycle is 2 years), and the annually replaced waste antifreeze will be increased with rapid increase of China's automobile population. The waste antifreeze is classified as a dangerous waste in Scrapped Motor Vehicle Disassembly Environment Protection Technical Specification of Environment Protection Industry Standards HJ348-2007 of the People's Republic of China. Thus, harmless and resourceful treatment and utilization of the waste antifreeze are put on the agenda.
The existing technologies and studies mainly focus on recycling the waste antifreeze or extracting ethylene glycol therein for use. Chinese invention patent ZL 95114044.2 discloses a waste antifreeze regenerating method: classifying waste antifreeze based on colors, measuring various metal corrosion and pH value, adding a flocculant, precipitating impurities, adding a preservative, an anti-rust agent and the like, adding an antifreeze agent and a dye, and then testing the antifreeze, and the antifreeze qualified upon testing is reused as automobile antifreeze In practice, antifreeze of different colors or brands, due to different components, generally react to generate gel or precipitates after being mixed, and similar problems can be avoided to a certain degree by classification based on the colors of the antifreeze, but the operation in the practical recovery flow is difficult, and the implementation is unattainable.
Chinese patent CN 203043722U discloses a waste antifreeze regeneration and filtration device composed of an adsorption layer, a filtration layer and an oil absorbing layer, wherein waste antifreeze from which various impurities, engine oil and the like are removed is used as a production raw material of automobile antifreeze Chinese patent CN 203999444U discloses a device for recovering ethylene glycol from waste automobile antifreeze, which is composed of a liquid storage tank, an alkali reactor, an acid reactor, a pressurizing and heating component, a flash tank and a reboiler, wherein recovered ethylene glycol is obtained after the technical measures of acidification, alkalization, pressurizing and heating, gas-liquid separation, flash evaporation and the like; and the recovered ethylene glycol can be reused as antifreeze or a raw material of other process products. The automobile antifreeze is sold to terminal customers in the form of small packages (4 L or 1 L), the price difference between renewable antifreeze and common non-renewable antifreeze is not obvious, and due to uncertainty about the quality of renewable products, customers tend to purchase the common non-renewable antifreeze with slightly higher price.
Ethylene glycol serving as a main component of the waste antifreeze is a main grinding aid raw material of a cement grinding aid. U.S. Pat. No. 2,225,146 discloses a method for preparing a cement grinding aid with alcohols (e.g., ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, etc.). U.S. Pat. No. 2,225,146 discloses a method for preparing a cement grinding aid with ethylene glycol and acetate of the ethylene glycol. Chinese patent CN94113758.9 discloses a hydraulic cement accelerator doped with polyols, containing a well-known accelerator and low molecular weight polyols (e.g., glycerol and ethylene glycol), and such an admixture is effective for shortening the initial setting time of hydraulic cement, mortar and concrete and is also beneficial as a low-temperature accelerator; and a preferred embodiment may also include components selected from some alkanol amines or a mixture thereof. Other components including metasilicate, phosphate, borate, nitrite or triethanolamine or the like in the waste antifreeze is often used as an early strength agent, a retarder or an inhibitor of cement concrete; silicone, alcohols, glycidyl ether and the like used as defoamers are also used as defoamers in cement concrete admixtures. Thus, the waste antifreeze can be used for preparing a cement grinding aid after residual heavy metal ions (e.g., copper ions, hexavalent chromium, etc.) as well as engine oil and solid impurities added in the waste antifreeze recovery flow are removed via appropriate technical processes.
In most of the existing technologies and studies, the waste antifreeze is regenerated into new antifreeze via the technical measures of acidification, alkalization, pressurizing and heating, gas-liquid separation, flash evaporation and the like or ethylene glycol is extracted from the waste antifreeze for secondary sale, the treatment process is complex, the equipment investment is high, the energy consumption is high and the economic benefit is not obvious.